Right. There have always been novel concept planes but they usually fall apart for practical reasons * SSTs like Concorde use a lot more fuel and have to be n

Right. There have always been novel concept planes but they usually fall apart for practical reasons * SSTs like Concorde use a lot more fuel and have to be narrow, to the point of sacrificing comfort * blended wings are not desirable for passenger comfort; people like windows and hate middle seats * airplanes have to fit within the constraints at operating at airports that currently exist. Cities are not going to build new airfields or modify existing ones for billions of dollars for what might be a technological fad instead of a long term improvement, so you pretty much need to fit existing gates, existing runway widths and weight limits, etc. The A380 needed such modifications and therefore could not be flown everywhere.